STUDIES ON CEYLON H.EMATOZOA. 759 



The lite-cycle of H. nicorite at once recalls the processes 

 observed in Coccidia, but there are two points of difference 

 which are, I think, important as diagnostic cliaracters. 

 Firstly, at no stage does H. nicorite show in its nucleus the 

 Icaryosoine so characteristic of the coccidia; secondly, the 

 sporozoites are not enclosed in a resistant cyst, and become 

 motile within a relatively short time after they ai^e formed 

 without the stimulus of transference to another host-indi- 

 vidual. In all the coccidia hitherto described the sporozoites 

 remain dormant, until by one means or another they pass to 

 the exterior, and are taken up by another individual of suit- 

 able species where the sporozoites are set free. As regards 

 the question as to whether the stages in the leech might not 

 belong to an independent parasite, and have no connection 

 with H. nicoriai, the following points may be urged: The 

 close correspondence between the stage of digestion and the 

 development of the parasite, the strong morphological resem- 

 blance between such stages as those figured in figs. 1, 2, '3, 

 9a, 25, 26, 28-34, 38-41, 51, 54-56, derived respectively 

 from the blood of the tortoise and different parts of the leech, 

 and the apparent absence of the parasite in leeches taken 

 from uninfected tortoises. Lastly, on the hypothesis that 

 the stages in the leech are independent of those in the 

 tortoise, the only other group in which the forms from the 

 leech could be placed is tiiat of the Coccidia. The points of 

 divergence noted in the preceding paragraph are, I think, 

 sufficiently importnnt to distinguish them from any form 

 belonging to that group. The point is, of course, one which 

 could be determined experimentally when suitable material is 

 available. 



Lister Institute, 



April, 1910. 



